Answer: 25 grapefruits
Step-by-step explanation:
They buy grapefruit at a price of 5 per dollar. This means that the price per grapefruit is:
= 1 / 5
= $0.20 per grapefruit.
They then sell at a price of 5 per $3. The selling price per grapefruit is:
= 3 / 5
= $0.60
The profit per grapefruit is:
= 0.60 - 0.20
= $0.40
In order to make a profit of $10, they should sell:
= 10 / 0.4
= 25 grapefruits